Add IdentitySafeLogging trait to sanitize logs

This removes sensitive information from the logs.
Add safe logger to other parts of Identity
Update logging in Identity API client now uses safelogger
Add log sanitisers for some sensitive JSON strings
Remove SafeLogger factory method

Encourage people to use SafeLogger as a mixin. This is achieved by
having SafeLogger explitictly replace the Logger found in the client.
Config for page search size
Merge branch 'master' into fronts-tools-search
Paginated search
Better messages
Add logging to Futures in parseResponse
Add what was failing to log messages
Related headline trails have the right heading level
Show the right trailblock template when video is linked
Do not display any image if it is our fallback
Clipboard accepts droppable external content
Add clear fix to article contain to prevent leakage.
Merge pull request #1452 from guardian/inline-images

Add clear fix to article contain to prevent leakage.
Indentation fix
Merge pull request #1454 from guardian/frontsFeatures

Indentation fix
Use an option to detect fallback image